/Engine/Source/Runtime/InteractiveToolsFramework/Public/BaseGizmos/GizmoMath.h
Project the input Point onto the plane defined by PlaneOrigin and PlaneNormal,
Nearest position to Point lying in the plane
namespace GizmoMath { FVector GizmoMath::ProjectPointOntoPlane ( const FVector & Point, const FVector & PlaneOrigin, const FVector & PlaneNormal ) }